Navigation and Manipulation for Autonomous Underwater Dismantling of Offshore Structures

Christian Welch, S.M., 2015Franz Hover, Advisor

The dismantling of offshore structures is a complex task in the oil and gas industry, driven by strict environmental standards. Autonomy presents itself as a solution to do this as cost-effectively and safely as possible, by taking ROVs and divers out of the equation. In this thesis, three avenues are researched: navigation, attachment, and manipulation. First, the Iterative Closest Point method is investigated as a means to correct position drift of an inertial navigation system. Using a previously obtained 3D sonar map from a real worksite, the algorithm is able to reconcile dead-reckoned pose to an accuracy of ~7cm from a 100k-point sonar scan. Second, to attach lifting points to subsea scrap without bracing onto it, a single mechanism was designed to both drill and affix anchors in a single penetration, from a vehicle in free flight. A prototype was fabricated and its functionality verified. Third, to promote robust and stable robotic interactions using an industry standard non-backdrivable manipulator, a control law was developed to have the system passively interact with its environment, by mimicking an arrangement of masses, springs, and dashpots. This control law was tested in a simple experiment that achieved a 90% reduction in settling time.